This invention relates to the field of welding and particularly to laser welding. Many different heating sources have been used for welding. Among the most common are combustible gases, electrical resistance (for spot welding), electric arc, and friction. With the development of lasers in recent years, coherent light has become a viable welding source as well. A laser provides a unique source of radiant energy whose intensity and position can be precisely controlled. In laser beam welding, the beam is focused near the surfaces of the materials to be joined and the beam is moved to melt the advancing metal and form the weld. An inert gas atmosphere may be provided to protect the hot metal from oxidation. In some applications, a mild stream of inert gas is used to provide oxidation protection as well as to promote "keyholing", i.e., a deep penetration mode in which the laser melts a small cylindrical volume through the thickness of the material. For a general overview of laser welding, see Laser Beam Welding in Metals Handbook, Ninth Edition, Volume 6, Welding, Brazing and Soldering, Pages 647 to 671 (American Society for Metals, 1983 ).
Although lasers have been used successfully to weld many different metals, there exists a continuing need to apply laser welding techniques to additional alloys and joint configurations. Additionally, there is a need in the laser welding field to improve the quality and producibility of laser welds by eliminating cracking, insufficient penetration, blow holes, porosity, and other quality problems.